1. Field of the Invention
This invention is related to apparatus for automatically joining two boards in an end-to-end union, and in particular to apparatus for curing adhesive applied to the union of two boards of lumber mated end-to-end in a finger joint union.
2. Description of the Prior Art
Short pieces of lumber may be joined end-to-end in a finger joint union to produce a long length of lumber. The end portions of the boards are machined to form mating finger joints which are coated with an adhesive and are compressed to close the joint. The jointed lumber set is subsequently cured by compressing the glue joint with a resistance heater ram, or by passing the mated joint through an electrical field in which radio frequency current is conducted through the finger joint union for the purpose of curing the adhesive.
In the high speed, high volume continuous production process, conveyor equipment automatically mates the end finger joints of longitudinally moving boards and then applies pressure necessary for closing the joint. In this procedure, several random length sections of lumber are joined together to form a continuous board, and the glue joints are cured by advancing the jointed boards through a long curing chamber in which the glue joints are subjected to an intense radio frequency field.
A limitation to the continuous flow curing process is that pressure is applied through the union only in the axial direction. A stronger glue bond between the jointed fingers can be obtained by compressing the union axially and orthogonally, with the result that the properly cured jointed union can withstand higher bending stress concentrations, and thereby qualify for use as a higher grade of structural lumber.
Lumber assembly apparatus has been provided for producing finger jointed lumber on an intermittent basis in which the flow of lumber is halted during the curing step so that the finger joint union can be compressed axially and orthogonally while the adhesive applied to the finger joint is cured. Although the conventional "stop and go" process yields a superior finger joint, production volume of the jointed lumber is substantially reduced because of the curing time required for each joint.